The present invention relates generally to self metrology of optical projection lithography systems, and more specifically, to a method and apparatus for analyzing the aerial image of such a system using a subwavelength slit.
As the feature sizes on integrated circuit devices have grown ever smaller, the demands on the optical train in the optical lithography system have grown ever greater. This has led to an increased need for techniques for accurate and real-time monitoring of the optical system's performance.
In a typical prior art technique for monitoring system performance, a reticle pattern is imaged onto a resist coated substrate. The substrate is then developed and used to analyze the optical system's performance. The analysis is based on the pattern being a convolution of a perfect image of the reticle and the performance characteristics of the stepper's optical system. Unfortunately, the nonlinear qualities of the photoresist technique adds a third variable making it difficult to accurately reduce the data and derive the performance of the optical system. A further problem with this method of analysis is that it is slow and time consuming.